1. Field of the Invention
The present invention relates to a medical image display apparatus.
2. Description of the Related Art
A magnetic resonance imaging device (MRI device) as a medical image generating device can take a large variety of images such as longitudinal relaxation enhancement (T1) images, transverse relaxation enhancement (T2) images, proton density images, fluid attenuated inversion recovery (FLAIR) images, fat suppression images, diffusion weighted imaging (DWI) images, perfusion weighted imaging (PWI) images, functional images (f-MRI images), and magnetic resonance (MR) spectroscopy (MRS) images. An X-ray computed tomographic (CT) imaging device (X-ray CT) is sometimes used to take a plurality of types of functional images such as blood flow images as well as general anatomical images based on CT values. In many cases, films are arranged side by side and displayed on a viewing screen. An increasing number of apparatuses are designed to capture multi-modality images of the same subject to be examined and display them.
In performing radiographic interpretation, a doctor displays a plurality of types of images concerning the same region upon arranging them on a film or monitor, and observes them while moving his/her viewpoint to a place corresponding to the same anatomical region. Methods of comparing monochrome or color images upon superimposing them (fusion method) instead of arranging them at different positions have already been reported and generally used in X-ray CT, SPECT (Single Photon Emission Computed Tomography), and PET (Positron Emission Computed Tomography) (see non-patent references 1 and 2). Such methods have already been executed in MRI by using products on the market and free software for f-MRI and MRS (see non-patent reference 3).
In a current radiographic interpretation technique based on “diagnosis by arranging and comparing a plurality of types of images”, since a doctor interprets a plurality of types of images while moving his/her viewpoint, eye strain occurs, resulting in requiring a long period of time for radiographic interpretation. This situation also applies to the monitor of a display apparatus instead of films. In addition, when images are compared with each other upon being arranged side by side, since the viewpoint of the doctor moves, it is difficult to perform diagnosis by anatomically precise comparison. In some dynamic display techniques, images are sequentially displayed in the same frame in a spatial slice direction or time axis direction due to the situation in which the corresponding logical files are arranged on a disk or display memory in the corresponding direction. However, such a function is not created as an intentional function, and hence images cannot be displayed in various orders. Although a multi-frame display technique is available, frames are arranged in a slice direction or parameter direction.
In many cases, images to be compared are arranged at anatomically different slice positions because of limitations on imaging conditions. In addition, in echo planar imaging (EPI) and the like, the distortions of images are large as compared with spin echo (SE) images and the like, and hence it is difficult to compare the images.
When sensed images are to be simply displayed side by side, images vary in luminance or color unless they are normalized depending on the target. This makes it difficult to objectively observe the images. In the case of an MR technique, it is said that luminance information can be determined at about three levels at best, namely white, gray, and black. According to the fusion method, since images are superimposed on each other, one of images to be superimposed is limited to one which has a small spatial resolution or locality. In some cases, when, for example, images each having constant as a whole, e.g., T1 enhancement images and T2 enhancement images which are routinely used in MRI, are to be superimposed, it is difficult to grasp their relationship. The number of types of images which can be discriminated after they are superimposed on each other is two at best. This technique is not suitable for the types of images which are not generally colored. The following are the main prior art references:
Ratib O, “PET/CT image navigation and communication”, J Nucl Med. Jan; 45 SuppII: 46S-55S (2004),
Joseph Hajnal, D. J. Hawkes, Derek Hill, J V Hajnal, “Medical Image Registration”, CRC Press, and
Friston K J, Ashburner J, Poline J B, Frith C D, Heather J D, Frackowiak R S J, “Spatial Registration and Normalization of Images Human Brain Mapping 2,” 165-189 (1995).